1. Field of Disclosure
The present disclosure relates generally to inkjet printers, and more particularly, to ejection devices for inkjet printers and a method for fabricating the ejection devices.
2. Description of the Related Art
A typical ejection device (printhead) of an inkjet printer includes an ejector chip, a nozzle plate either attached or formed with the ejector chip, and a Tape Automated Bond (TAB) circuit for electrically connecting the ejector chip to the inkjet printer during use. The ejector chip may be fabricated using a silicon substrate (wafer) having a plurality of fluid ejecting elements adapted to eject a fluid (such as ink). Further, the ejection device may also include flow features (fluid chambers and fluid supply channels) formed in a thick film layer deposited on the silicon substrate and below the nozzle plate. Alternatively, the flow features may be ablated along with nozzles of the nozzle plate. The nozzle plate and the flow features may be formed of a polymeric photoresist material, i.e., an organic material.
Considering that various types of fluids may be used with the ejection device, compatibility between the fluids and the polymeric photoresist material of the nozzle plate and the flow features is of great significance, specifically, for the current Photo-Imageable Nozzle Plate (PINP) based ejection devices. Further, such compatibility is related to print quality and the service lifetime of the ejection devices. Specifically, an incompatible fluid may cause damage/degradation to the polymeric photoresist material of the nozzle plate and the flow features, thereby affecting the print quality and shortening service lifetime of the ejection devices.
Accordingly, significant efforts have been made to develop fluids that are compatible with PINP based ejection devices, and/or to develop polymeric photoresist materials with high chemical resistance towards the fluids. However, fluid stability has typically been compromised while developing better polymeric photoresist materials. Alternatively, mechanical properties of the polymeric photoresist materials have been sacrificed for achieving better fluid compatibility. Thus, such strategies have assisted in achieving improved ejection devices and print quality only to some extent.
Although current PINP based ejection devices work well with available aqueous fluids, fluid-nozzle incompatibility is still challenging for the advancement of PINP based inkjet technology. Further, it has been observed that polymeric photoresist materials of flow features and nozzle plates are easily attacked by surfactants; dispersants; other additives; and a few organic solvents such as humectants, which are used as fluid ingredients. Though some of such fluid ingredients are beneficial for fluid property modification in order to produce fluids with better functionalities (such as high reliability, quality jetting, high resistance to smear and so forth), however, the fluid ingredients may be unsuitable for being employed in current fluid formulation due to severe incompatibility with the current polymeric photoresist materials used for PINP based ejection devices.
For examples, higher content of 2-pyrrolidine that is used as a fluid ingredient may improve fluid jetting quality. Similarly, use of higher content of hexyl carbitol as a fluid ingredient may improve fluid drying time on a print medium, such as paper. However, the use of the aforementioned materials in the fluids has resulted in damage to the current materials used for PINP based election devices. Specifically, such materials act as attacking organic ingredients that are capable of penetrating into the polymeric photoresist materials of the nozzle plates and the flow features to dissolve and soften the respective polymeric network, thereby resulting in reduced mechanical strength of the PINP based ejection devices along with deterioration of fluid ejecting (jetting) performance.
Therefore, the PINP based ejection devices may find appropriate application only with benign aqueous fluids, but neither with aqueous fluids consisting of incompatible organic solvents nor with organic-based fluids.
Based on the above limitations, nozzle plates composed of inorganic materials (such as silicon oxide, silicon nitride and the like) have been employed in various currently available ejection devices. Specifically, the inorganic materials possessing high solvent resistance are suitable for both aqueous and solvent-based inks. However, pure inorganic nozzle plates (such as the nozzle plates composed of silicon oxide/silicon nitride) may only have a limited thickness (below about 10 microns) due to an extreme slow deposition and etching rates for the inorganic materials. Further, nozzle plates composed of inorganic materials have high fragility due to residue stress and an extremely thin format.
Similarly, various other fluidic structures (re flow features and nozzle plates) have been formed by depositing a thick layer of an inorganic material (such as oxide/silicon nitride) on substrates. However, formation of such fluidic structures requires processing of thick layers that is associated with long deposition and etching time. Further, such thick layers easily tend to crack due to stress build-up. Additionally, it is difficult to create retrograde nozzles, which is important to eject stable fluid drops. Moreover, formation of such fluidic structures involves creation of deep trenches. However, these deep trenches may serve as areas for fluid entrapment. Further, maintenance of the fluidic structures, by techniques such as wiping, becomes difficult due to the presence of deep trenches.
Furthermore, fluidic structures that incorporate organic materials in nozzle plate and fluid chamber wall have also been formed. Such fluidic structures include an inorganic layer located on the nozzle plate and the fluid chamber wall, to improve adhesion between a substrate and the nozzle plate. However, various portions (such as a top portion and inner portions) of the nozzle plate and nozzles thereof are exposed to the atmosphere, thereby, making the fluidic structures vulnerable to a working fluid that is capable of degrading the organic material.
Other alternate fluidic structures have been formed by planarization of a surface of an ejection device by filling trenches with a polymeric material (organic) and covering a top surface with an additional layer as a thin nozzle plate. Since the thickness of the nozzle plate generally determines the nozzle length, it is difficult to create long nozzles that are required for either ejecting large fluid drops or improving the directionality of the ejected fluid drops, while using such fluidic structures.
Accordingly, there persists a need for effective and efficient ejection devices for inkjet printers, and a method for fabricating the ejection devices, for achieving better and long-lasting fluid compatibility with fluidic structures (nozzle plate and flow features) of the ejection devices, to prevent damage/degradation to the fluidic structures and fluid entrapment within the fluidic structures. Further, there persists a need for an effective and efficient method for fabricating ejection devices in order to form long nozzles in nozzle plates for either ejecting large fluid drops or improving the directionality of the ejected fluid drops.